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WayneBearCal



Joined: 09 Apr 2014
Posts: 33



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PostPosted: 12/15/14 12:27 pm    ::: Note to All Bracketologists Reply Reply with quote

I just noticed that the NCAA has already begun providing their official RPI data for WBB. This includes not only the listing of all teams in RPI order, but also the Nitty Gritty report and the individual team sheets.

In the past, we had to wait until January for this data. And the overall RPI list was only updated once a week on Mondays, and the other reports were issued on an irregular basis (including one season where they didn't even bother to post the season-ending reports which were used by the committee during final deliberations). This season, it appears that the overall RPI is being updated daily, and the Nitty Gritty and team reports are being issued weekly.

Personally, I prefer this official data because I want to see what the committee uses, and the alternative sources have always been lacking. WBBState uses raw rather than adjusted RPI, RealTimeRPI has had too many errors in the past, and while WarrenNolan is generally the most accurate, their nitty gritty and team reports are not the same format as the NCAA's.


For the overall RPI listing, go to:
http://www.ncaa.com/rankings/basketball-women/d1/ncaa-womens-basketball-rpi

For the Nitty Gritty and team sheets, go to:
https://rpiarchive.ncaa.org/default.aspx

and set the parameters as follows:

Select Division: I
Select Sport: Basketball
Select Gender: Women
Select Report: Current
Select Document: Use either Nitty Gritty or Team Sheets
Enter Year: 2015

I did notice that there are some errors in some of the team sheets ("Last 10 Games" record is erroneous for some teams), but otherwise the sheets looked mostly accurate at first glance. If you notice other errors, please report.



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Avatar: Paige Bowie, Jennie Leander and Lauren Ashbaugh celebrate after Cal's upset of #9 Colorado State on December 21, 1998
beknighted



Joined: 11 Nov 2004
Posts: 11050
Location: Lost in D.C.


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PostPosted: 12/15/14 3:03 pm    ::: Reply Reply with quote

I was pleased to see this, particularyl because there hasn't been a really great source for all of the information since Jerry Palm stopped doing WCBB.

BTW, I'm not sure what you mean when you say that WBBState doesn't do adjusted RPI. So far as I can tell, they seem to use the same formula as the NCAA.

Edited to add:

WBBState does, however, keep doing the RPI calculation during the postseason, so its final RPI ends up being different from the NCAA's.


WayneBearCal



Joined: 09 Apr 2014
Posts: 33



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PostPosted: 12/15/14 8:09 pm    ::: Reply Reply with quote

beknighted wrote:
... BTW, I'm not sure what you mean when you say that WBBState doesn't do adjusted RPI. So far as I can tell, they seem to use the same formula as the NCAA ...


At WBBState, when you click on the Standings tab and select Ratings Percentage Index, you get the list of all teams with columns beginning with "RPI" then "Raw RPI". I had always assumed they were using the term Raw RPI to indicate that they were not using the same total adjustments used by the NCAA. And indeed you can see the numerical differences for individual teams between the Raw RPI and the RPI as calculated by WarrenNolan.com, which as I said is the most accurate. (Since WarrenNolan updates throughout the day, maybe you want to wait until early morning to compare the numbers.)

You can also do an early morning comparison of the official NCAA rankings with WarrenNolan, WBBState, and RealTimeRPI. When you start going down the respective lists (who's ranked #1, #2, etc.), the lists may seem the same at first but eventually you'll notice a whole bunch of discrepancies. Historically, I've found WarrenNolan to be by far the most accurate, with WBBState and RealTime RPI well behind.

These minor differences shouldn't matter, but realistically when the committee is trying to sort and rank a whole bunch of teams at once, there's an overwhelming (and unfortunate) temptation to resort to the shorthand of comparing teams on RPI-based stats such as record vs. Top 25 RPI, Top 50 RPI, defining bad losses based on RPI > 100 or 150, etc. So from that standpoint it's important to make sure that you're using the correct RPI standings. Of course, the whole issue is moot now that the NCAA is updating WBB RPI more frequently (and hopefully will continue to do so daily).



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Avatar: Paige Bowie, Jennie Leander and Lauren Ashbaugh celebrate after Cal's upset of #9 Colorado State on December 21, 1998
SpaceJunkie



Joined: 10 Sep 2012
Posts: 4241
Location: Minnesota


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PostPosted: 12/15/14 8:30 pm    ::: Reply Reply with quote

Since I'm an ignoramus on the subject, what's the difference between Raw RPI & Adjusted RPI?


WayneBearCal



Joined: 09 Apr 2014
Posts: 33



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PostPosted: 12/15/14 9:23 pm    ::: Reply Reply with quote

SpaceJunkie wrote:
Since I'm an ignoramus on the subject, what's the difference between Raw RPI & Adjusted RPI?


I really don't know what WBBState means when they use the term "Raw RPI". Some people use that term to describe a team's actual numerical percentage derived from the RPI formula (e.g. .6255) instead of the ranking (#18 out of 349 teams). So it's possible that WBBState is indicating that they ARE providing the correct RPI as computed by the NCAA. But their numbers are consistently different from WarrenNolan's, and the team rankings are not the same as derived by the NCAA. So that's why I wondered whether they were simply not making the same adjustments that the NCAA makes (i.e. giving different weights to results based on whether the team was at home, on the road, or on a neutral court).

There are many data errors that can cause one provider's RPI to be different from the NCAA's. Obviously someone could have recorded the wrong result (win, loss, or game cancelled). Or more often they use the wrong venue (assume that one team is the home team when in fact the game was played on a neutral court). And when there are teams who recently made the transition to Division I, sometimes an opponent's record will still show them as having played a non-Div I team. I've seen these errors on RealTimeRPI's data in the past, less often on WarrenNolan's data, and never really checked WBBState's data that carefully because their team results pages are a bit too busy for easy scanning.



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Avatar: Paige Bowie, Jennie Leander and Lauren Ashbaugh celebrate after Cal's upset of #9 Colorado State on December 21, 1998
SpaceJunkie



Joined: 10 Sep 2012
Posts: 4241
Location: Minnesota


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PostPosted: 12/16/14 1:56 am    ::: Reply Reply with quote

WayneBearCal wrote:
SpaceJunkie wrote:
Since I'm an ignoramus on the subject, what's the difference between Raw RPI & Adjusted RPI?


I really don't know what WBBState means when they use the term "Raw RPI". Some people use that term to describe a team's actual numerical percentage derived from the RPI formula (e.g. .6255) instead of the ranking (#18 out of 349 teams). So it's possible that WBBState is indicating that they ARE providing the correct RPI as computed by the NCAA. But their numbers are consistently different from WarrenNolan's, and the team rankings are not the same as derived by the NCAA. So that's why I wondered whether they were simply not making the same adjustments that the NCAA makes (i.e. giving different weights to results based on whether the team was at home, on the road, or on a neutral court).


After looking through, it looks to me that the only reason for the difference in WBBState's RPI is because they calculate the Opponents' Opponents' Winning Percentage for teams differently than NCAA does. I should e-mail WBBState to find out if they're doing it wrong.


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